function  fr() {
    const v = new Promise((resolve,reject)=>{
        setTimeout(()=>{
            var a = 'hello'
            resolve(a)
        },10)
    });
    return v
}

var n = fr().then((val)=>{
        return new Promise((resolve,reject)=>{
            setTimeout(()=>{
                var a = val + 'lagou'
                resolve(a)
            },10)
        });
})

var m = n.then( (val)=>{
    return new Promise((resolve,reject)=>{
        setTimeout(()=>{
            var a = val + 'I ♥ U'
            resolve(a)
        },10)
    });
})

m.then( (val)=>{
    console.log(val)
})
